# All Questions

134,312 questions
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### When will Hund's rules fail?

I heard someone mentioned that Hund's rules do not always work. Looking at atomic spectrum: (https://qudev.phys.ethz.ch/phys4/PHYS4_lecture10v1_2page.pdf page 10 Hg spectrum) How could singlet (with ...
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### How to calculate electrostatic potential at a point w.r.t an ensemble of point charges?

Given an ensemble of charges, how to derive the electrostatic potential at any point due to the ensemble? For example, consider six point charges, each approaching the origin along the three co-...
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### Differential equations for the LC circuit

On wikipedia one can find that the DE for an LC circuit is given by $$\ddot I+\frac{1}{LC}I=0$$In one of my papers however I found the equation $$\ddot Q+\frac{1}{LC}Q=0$$ and I've been confused by ...
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### A balloon is descending with 10m/s. When it is at 100m from the ground, a stone is thrown. Calculate the velocity of the stone at 20sec [on hold]

Assumed initial velocity of the stone to be 10m/s and found that it would cover 100m in about 3.585 seconds. But, the question is asking its velocity at 20sec.
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### Geant 4, simulate Tc-99m decay

I have a setup of Monte Carlo simulations in Geant4, and I'm able to simulate radioactive events from isotopes such as I-131 and F-18, which are defined in the RadioactiveDecayData5.2 files. Tc-99m ...
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### It is about Electrostatic Problem in electric field,flux [on hold]

Two point charges 16nC and 8nC are situated at the corners B and C of an equilateral triangle of side 0.03m. Find the magnitude and direction of the resultant electric field at the vertex A of the ...
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### Assuming standard pressure and temperature, how far would a given air molecule move in 1 hour

I'm trying to calculate how far a given Air Molecule would actually traverse in a room in 1 hour assuming standard states (i.e. thermal equilibrium and approximately standard temperature and pressure.)...
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### Time units in simulation

I am hoping that someone could give me some insight about my problem. Currently I want to simulate the evolution of a gaussian wavepacket in a time-dependent potential using the Crank-Nicolson scheme. ...
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### Bond graph, how to use it? [on hold]

Yesterday I heard the word "bond graph" and I felt like searching a bit about it. From what I understood, it is a graph that links the flow of energy between "states" in multiphysics systems. I am ...
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### What are the differences between a Michelson and Self-Mixing interferometer?

I'm approaching to interferometric devices. I would say that Michelson interferometer uses a laser source and a "discrete" system of mirrors and other optical components such lenses and screens. On ...
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### Wave-like properties of particles [duplicate]

If we consider a particle such as an electron to have wave-like properties too, what kind of wave it is? What is exactly meant by its wavelength?
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### Does pressure decreases in accelerating fluids?

Bernuolli says that in a pipe when speed increases pressure also decreases and that happen when pipe become narrower. So,if a fluid accelerate (increases speed) due to ...
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### General derivative of the exponential operator w.r.t. a parameter

I am interested in the calculation of the general $N$th derivative w.r.t. a parameter $\lambda$ of a quantum mechanical exponential operator with the following structure: \begin{equation*} \frac{\...
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### What is the different of imaging using Ultrasound and Terahertz radiation [on hold]

Right now, I am developing an ultrasound NDT system for crack detection in railway track. Then, I read about terahertz imaging, I am really curious what is the different between terahertz imaging and ...
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### Electromagnetic field tensor and antisymmetry

Why does the inner product between the four force (caused by the electromagnetic field tensor) and the four velocity equaling zero imply that the electromagnetic field tensor is antisymmetric? This ...
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### what's the main difference between electrostaic potential,potential difference and electrostatic potential energy? [duplicate]

Please make it possible to grasp in layman terms,in terms of everyday life with good examples.
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### Understanding the variational / functional derivative (in relation to the Euler-Poincaré equation)

I'm trying to understand the Euler-Poincare equations, which reduce the Euler-Lagrange equations for certain Lagrangians on a Lie group. I'm reading Darryl Holm's "Geometric mechanics and symmetry", ...
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### Distance between the luope and the virtual picture: I can not see any

I have a biconvex lens. f=45mm. (This is a loupe). I have an object (G). This object is G=64mm broad. When I place this object in a distance of g=42mm in front of the lens I get a virtual picture. I ...
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### Convert negative parameters of Altitude Height into possitive using BMP180 Sensor

I am using BMP180 I2C sensor interface with Arduino and with the help of mentioned below code ...
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### NPN transistors voltage drop between base and collector

Well I understand why if we increase the voltage between the emmiter and the collector the base current is reduced (it is reduced because the reverse bias depletion region width is increased so less ...
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### Is it possible for electromagnetic waves in the Extreme Low Frequency range to carry HQ video and audio signals? [duplicate]

I had just finished this interesting read on a us navy project and was wondering how Brain computer interfaces are touting in the near future to pick up thoughts that might need the same bit rates as ...
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### Electric field on dipole with different directions [on hold]

Griffith's E&M problem 4.5 page 165 In the figure p1 and p2 are perfect dipoles a disantce r apart. What is the torque on p1 due to p2.? Wjat is the torque on p2 due to p1? well i calculated ...
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### Resistor Capacitor circuits

I am a high school physics teacher and came across some issues today that I am unable to explain. We made a circuit with an $11$ V power source connected to a $100~k\Omega$ resistor and $100~\mu F$ ...
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### how spinfull chains in 1d are possible since spin is not well defined in 1d?

as far as I know, in QM spin is not defined in 1d, because of algebra$\mathfrak{su}(2)$ can not be satisfied in 1d. however we talk about spin chains, spinfull luttinger liquids in 1d all the time. I ...
Based on Lorentz factor $\gamma = \frac{1}{\sqrt {1-\frac{v^2}{c^2}}}$ it is easy to see $v < c$ since otherwise $\gamma$ would be either undefined or a complex number, which is non-physical. Also, ...